When Hib vaccine is given together with the inactivated polio vaccine (IPV), significantly fewer Hib antibodies get produced than would be produced if it were given with a live polio vaccine. It was also found that children that are given Hib and DTaP vaccines at the same time develop significantly fewer tetanus antibodies.
Injection sites were different for the vaccines (one in the arm, and other in the leg). It was previously unknown that giving two vaccines at the same time causes immune interference between them. The biological mechanism of this phenomenon is unknown.
DTaP/Hib combined vaccine produces significantly fewer Hib and tetanus antibodies than would be produced if they were given separately. More: , , .
Nevertheless, in almost all countries, Hib is part of a penta- or hexavalent vaccine, together with IPV and tetanus (Pentacel, Infanrix, etc.)
- DTaP/Hib combined vaccine (with acellular pertussis vaccine) produces 10 times less Hib antibodies than DTP/Hib combined vaccine.
- If the injection site for Hib and DTaP vaccines is the same then 5-15 times less Hib antibodies developed, as compared to choosing different injection sites for the two vaccines.
- DTaP produces significantly fewer diphtheria antibodies than DTP.
After England switched to the acellular pertussis vaccine (DTaP/Hib), an almost 7-times increase in Hib incidence was reported.